The US military has re-entered Iraq and launched air strikes after President Barack Obama authorised military intervention to relieve a siege on tens of thousands of civilians trapped on a barren mountain and halt the advance of militant Islamist fighters.

Less than three years after it withdrew its combat troops after a long and bloody occupation, the US intervention comes as Islamic State (formerly known as ISIL or ISIS) forces have captured swaths of northern Iraq.

Islamic State, which counts about 60 Australians among its fighters, was a “highly potent insurgent army” capable of imposing its “abhorrent form of government” and forging alliances with other extremist organisations, Mr Abbott said.

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Mr Obama rose to political prominence opposing the Iraq war and took the presidency vowing to end it. He also resisted intervening militarily as the Syrian conflict spun out of control and into the hands of Islamist militants.

The difference now, he suggested, was a looming “genocide” as members of the Kurdish Yazidi religious minority fled to Mount Sinjar amid threats from Islamic State militants to exterminate them.

A F/A-18E Super Hornet takes off from aircraft carrier USS George H.W. Bush in the Gulf, as US air strikes in Iraq begin. Photo: AFP/US Navy

The Yazidi - who practise a variant of the ancient religion of Zoroastrianism - were “hiding high up on the mountain, with little but the clothes on their backs”, Mr Obama said.

He described reports of “militants rounding up families, conducting mass executions, and enslaving Yazidi women”.

“They’re without food, they’re without water,” he said. “People are starving and children are dying of thirst. These innocent families are faced with a horrible choice: descend the mountain and be slaughtered, or stay and slowly die of thirst and hunger ...

US President Barack Obama: “When we have the unique capabilities to help avert a massacre, then I believe the United States of America cannot turn a blind eye.” Photo: Reuters

“When we have the unique capabilities to help avert a massacre, then I believe the United States of America cannot turn a blind eye.”

Late on Thursday, two US aircraft dropped 500-pound laser-guided bombs on artillery being used against Kurdish forces defending the city of Arbil, a Pentagon spokesman said.

Earlier, three US transport aircraft, protected by FA-18 fighter jets, dropped 8000 Meals Ready-to-Eat - US military ration packs - and about 20,000 litres of water to the Yazidis. Earlier reports said 40 women and children had already died of hunger and thirst, with temperatures reaching more than 45 degrees during the day.

In the coming days, Iraqi government and Kurdish fighters hope to open a safe corridor to evacuate the civilians.

The US is alarmed that Islamic State cadres continue to make gains in Iraq. With the major city of Erbil now under threat, Mr Obama has said US warplanes will also be directed to protect the Kurdish metropolis from the extremists.

US military advisers remain in the city, although consulate staff left in June. Mr Obama said the planes would protect all US government personnel in Iraq.

However, he has not authorised US troops on the ground. Australia, meanwhile, is not providing any military support. The security of Australian diplomatic staff in Baghdad was being monitored “closely”, a Department of Foreign Affairs spokesman said.

Labor leader Bill Shorten supported the US intervention and called on Mr Abbott to restore the $7.7 million humanitarian aid budget for Iraq, which was axed in the May budget.

The US President stressed this would be a “limited”, “targeted” mission and that it was up to the Iraqis to sort out their own affairs.

Mr Obama wants a change of government in Iraq, which has sowed discontent by favouring the Shiite majority. Iraq’s government is heavily influenced by Iran.

Islamic State espouses a brutal brand of Sunni Islam and has gathered some support from Iraqi tribal chiefs amid the divisions. It has committed a host of war crimes as it spread from Syria into Iraq, conducting mass executions of captured soldiers and police and posting the grisly footage on the internet.

The two leading US Republicans who have been most critical of the President’s withdrawal from Iraq and reluctance to use force, senators John McCain and Lindsey Graham, welcomed the intervention but called for an even greater commitment.

“A policy of containment will not work against [Islamic State]. It is inherently expansionist and must be stopped,” the senators said in a statement. “The longer we wait to act, the worse this threat will become, as recent events clearly show.”

But Australian National University strategic analyst Hugh White said there was no long-term military option to vanquish Islamic State and stabilise Iraq and Syria which didn’t involve deploying hundreds of thousands of troops.

“Nothing Obama does militarily will make a durable difference,” he said.

President Barack Obama has set no time limit on US air strikes targeting Sunni extremists in Iraq, despite fears that Washington is getting dragged back into conflict in the country.

"The president has not laid a specific end date," White House spokesman Josh Earnest told reporters, while insisting a "prolonged military conflict that includes US involvement is not on the table."

UK to drop food aid to Iraqi refugees

The British air force will drop food aid to Iraqi refugees fleeing extremists in "the next couple of days", the defence secretary says, although London has ruled out taking military action with the United States.

The announcement on Friday came after the Foreign Office urged Britons in the Arbil, Sulaimaniyah and Dohuk provinces of Iraq's autonomous Kurdistan region to "leave now" as fighting spreads north.

Prime Minister David Cameron said he was "extremely concerned by the appalling situation in Iraq and the desperate situation facing hundreds of thousands of Iraqis".

"And I utterly condemn the barbaric attacks being waged by ISIL (now Islamic State) terrorists across the region," he said in a statement.

The government's emergency committee, COBRA, met on Friday morning and agreed to help US humanitarian operations in northern Iraq and send the Royal Air Force (RAF) to drop food for stranded civilians.

The drops will be targeted at members of the minority Yazidi community who have fled from the extremists to the Sinjar mountains in northern Iraq.

"What we have decided today is to assist the United States in the humanitarian operations that started yesterday. We are offering technical assistance in that in terms of refuelling and surveillance," said Defence Secretary Michael Fallon.

"We are offering aid of our own which we hope to drop over the next couple of days in support of the American relief effort, particularly to help the plight of those who are trapped on the mountain."

A spokeswoman for Cameron's Downing Street office said however that Britain, which joined the US-led invasion of Iraq in 2003, was "not planning a military intervention".

WithAFP

Two aircraft dropped 500-pound laser-guided bombs on a mobile artillery piece near Arbil, Pentagon press secretary Rear Admiral John Kirby said in a statement.

Two aircraft dropped 500-pound laser-guided bombs on a mobile artillery piece near Arbil, Pentagon press secretary Rear Admiral John Kirby said in a statement.

Two aircraft dropped 500-pound laser-guided bombs on a mobile artillery piece near Arbil, Pentagon press secretary Rear Admiral John Kirby said in a statement.

10 Aug
Laying the groundwork for an extended airstrike campaign against Sunni militants in Iraq, President Barack Obama said Saturday that the strikes that had begun the day before could continue for months as the Iraqis build a new government.